Power semiconductor devices are widely used in fields requiring efficient electric power conversion. Fields in renewable energy have been attracting attention in recent years, such as photovoltaic generation and wind power generation; an in-vehicle field such as hybrid vehicles and electric vehicles; and a railroad field such as trains. The power semiconductor device includes switching elements and diodes that are incorporated therein. For the elements, Si (silicon) semiconductors have been conventionally used, but in recent years, wide band gap semiconductors such as SiC (silicon carbide) semiconductors have begun to be used. The SiC semiconductor has characteristics such as higher breakdown voltage, higher heat resistance and a lower loss than those of the Si semiconductor. The use of a SiC semiconductor in a power semiconductor device makes it possible to decrease the size of the power semiconductor device, and to reduce the loss in the device. Meanwhile, Si semiconductors are still widely used in power semiconductor devices. In that case, a power semiconductor element is sealed with a sealing material including epoxy resin which has good moisture resistance, heat resistance and mechanical properties.
However, the epoxy resin has a problem of insufficient adhesion to a resin case and/or metal members such as an electrode of a power semiconductor element, a conductive plate, a wire and pins used in a powered semiconductor device. Accordingly, the epoxy resin may have a risk of reducing the reliability of the power semiconductor device due to the insufficient adhesion.
An epoxy resin for sealing a semiconductor device has been known which contains, as an adhesion imparting agent, a nitrilotris(methylene)phosphonic acid salt which is a solid at normal temperature (see Patent Document 1, for example). Since, however, the organic filler of the phosphonic acid salt is mixed in the epoxy resin in this technique, this technique has disadvantages of insufficient adhesion strength because the phosphonic acid is unlikely to react with the base material and the epoxy resin, and insufficient long-term reliability because the cations of the phosphonic acid salt react with the epoxy resin, for example.